Demand for bandwidth is increasing and frequency bands are becoming more congested, especially in densely populated urban areas. One way to address this problem is to enable spectrum sharing and increase spectrum efficiency through better spectrum management. Diverse approaches to sharing spectrum bands include administrative, technical and market-based considerations.
The last few years have seen major activities and the development of the spectrum-sharing frameworks—in the 3.5 GHz band in the U.S. by the FCC and Licensed Shared Access (LSA) in the 2.3 GHz band in Europe by CEPT. Furthermore, the 3rd Partnership Project (3GPP)1, responsible for specification of the telecommunication/mobile systems, in its Release 13 has introduced License Assisted Access (LAA) feature to enable the operation of Long Term Evolution-Advanced (LTE-Advanced) in the unlicensed, 5 GHz band. These developments can be seen as a clear indication that major regulatory and standardisation bodies are embracing more comprehensive and systematic ways of spectrum sharing. 1 3GPP comprises of a number of telecommunications standards development groups and is responsible for specification of the telecommunication network technologies and wireless standards, including radio access, the core transport network, and service capabilities. 3GPP specifications address different generations of mobile systems, from 2nd generation—Global System for Mobile Communications (GSM), to 3rd generation Universal Mobile Telecommunications System (UMTS) and related technologies, to 4th generation-Long Term Evolution (LTE) and LTE-Advanced. Current work is focused on specifying 5th generation of mobile systems.
It is also recognised that not all shared spectrum resources will be the same. In some cases, sharing will be restricted in terms of types and the number of entities that are allowed to share spectrum, providing predictability in relation to the Quality of Service (QoS). The examples being licensed spectrum sharing in the 2.3 GHz band in Europe and Priority Access Licensee (PAL) in the 3.5 GHz band in the US. LSA enables the exclusive, shared use of spectrum between the incumbent and a licensed entity (in temporal and spatial domains). LSA, therefore, guarantees the QoS to both—the incumbent and the licensed entity. In the FCC model for spectrum sharing in the 3.5 GHz band, two lower tiers share the spectrum with the incumbent outside the exclusion zones. The incumbent is a top tier in this hierarchy and has a guaranteed protection from the tiers below. The middle tier (PAL) is protected from the interference caused by the third tier, but it has no protection from the transmissions by the incumbents.
In other cases sharing may be open to a number of systems, but without guarantees on the QoS—the example being WiFi® or third, General Authorised Access (GAA) tier in the FCC model.
A number of patent publications exist in the art. For example, patent application US 20150281971 A1 considers dynamic spectrum selection for a cellular network or user equipment, using centralised mechanism, wherein the decision on the shared spectrum selection is based on a most advantageous shared spectrum opportunity. While US 20150281971 A1 is based on cost minimisation, listing also required QoS, efficiency and amount of available spectrum as the selection criteria. PCT patent publication WO 2009/071431 (Ericsson) discloses a method for providing spectrum and infrastructure resources to shared spectrum operators, where the infrastructure resource may be provided using single or multiple base station. Spectrum resources may be allocated using one of the well-known access schemes—time-scheduling scheme, orthogonal frequency division or code division scheme. However, the Ericsson publication does not differentiate between different classes of shared spectrum. Instead, it provides a method for allocating spectrum to shared spectrum operators.
Furthermore, 3GPP Release 13 LTE-Advanced feature LAA incorporates operation in the unlicensed (shared) spectrum, while relying on the operation in the licenced spectrum, using Carrier Aggregation. LAA operation in the unlicensed 5 GHz band can be seen as an instance of a method that enables the operation using one class of shared spectrum, where multiple entities have right to access spectrum. This operation is supported by the operation in dedicated spectrum. However, LAA does not consider other classes of shared spectrum, where an entity has an exclusive right to access spectrum, such as LSA or PAL in the 3.5 GHz band in the US.
In addition to the above, the key technology trends are towards deployments of dense and ultra-dense networks of low power nodes (LPNs). For that reason, of particular interest are two baseband architectures that support such deployments of LPNs. These are the centralised baseband (CBB) architecture and distributed baseband (DBB) architecture. With CBB architecture, all the digital processing is performed centrally, whereas a radio unit that performs RF functions, together with the antenna, is located remotely. The example of CBB architecture are deployments featuring Remote Radio Heads (RRHs). RRHs may be high, or low-power nodes, with the radio unit that is, typically, located remotely. As such, the architecture featuring RRHs pose strict requirements on the throughput, and the acceptable delay and jitter between its radio and baseband units. Considering that digital signal processing functions are centralised, the architecture with RRHs is a predecessor of the Cloud-RAN architecture, allowing for centralised large-scale processing and cloud computing.
In the DBB architecture, each node performs all—baseband and radio functions. Small cells are an example of the DBB architecture. They can be connected to the core network and other radio network nodes using a range of different technologies, such as fibre, xDSL, or wireless.
Both architectures have their pros and cons. The CBB architecture enables pooling of resources, and the implementation of the advanced cooperative schemes that mitigate interference, at the cost of requiring high capacity, low-delay and low-jitter transport network infrastructure. The DBB architecture is a less costly alternative that enables mass deployment of small cells but does not offer all the advantages that come with centralised signal processing.
In view of all of the above, there is a need for a cellular operator to resort to shared spectrum, using different baseband architectures, and specifically to calculate shared spectrum resources required to meet certain QoS.